Fluid flow control for an aerofoil

Abstract

A device for influencing the wake flow of an aircraft wing having a high pressure side and a lower pressure side, the device including a body adapted for attachment in the region of the tip of the aircraft wing and having a through-duct with a first opening at a first end of the duct being located on the high pressure side of the wing and a second opening at a second end of the duct being located on the low pressure side of the wing, the duct being configured to permit a fluid flow through the duct so as to inhibit the flow of the fluid around the outboard extremity of the wing and to direct the fluid flow through the duct into a pair of opposing rotating flows of substantially equal magnitude externally of the duct.

The invention claimed is: 
     
       1. A device for influencing a wake flow of an aircraft wing, the aircraft wing having an inboard root end and an outboard tip end, a high pressure side and a low pressure side, and a leading edge and a trailing edge, the device comprising a body adapted for attachment in the region of the tip of the aircraft wing and having a through-duct with a first opening at a first end of the duct being located on the high pressure side of the wing and a second opening at a second end of the duct being located on the low pressure side of the wing, the duct being configured to, when the wing is exposed to fluid flow, permit a fluid flow through the duct so as to inhibit the flow of fluid around an outboard extremity of the wing and to direct the fluid flow through the duct into a pair of opposing rotating flows of substantially equal magnitude externally of the duct. 
     
     
       2. The device as claimed in  claim 1 , wherein the first opening of the duct is formed in part from: (i) an intake surface contoured to entrain oncoming fluid into the duct along an inboard region having a first pressure and to induce within a part of the fluid flow through the duct along the inboard region a first rotational component; and (ii) outboard edge comprising a formation configured to reduce an inlet velocity of fluid in an outboard region of the duct to thereby generate a region having a second pressure whose boundary is convex that induces within a part of the fluid flow through the duct a second rotational component opposite in direction to the first rotational component; the duct being configured to direct the parts of the fluid flow with the first and second rotational components out of the second opening into the pair of opposing rotating flows, the second pressure being higher than the first pressure. 
     
     
       3. The device as claimed in  claim 1 , wherein the duct has a plenum located between the first and second openings, and a first restriction located between the plenum and the first opening. 
     
     
       4. The device as claimed in  claim 3 , wherein an outboard wall of the duct defines a fluid-arresting structure configured to, when the device is exposed to fluid flow, generate a region having a second pressure within the duct that contributes to directing the airflow through the duct into a pair of opposing rotating flows of substantially equal magnitude externally of the duct, wherein the fluid-arresting structure defines an outboard edge of the first opening, and wherein the second pressure is higher than a first pressure at an inboard region. 
     
     
       5. The device as claimed in  claim 4 , wherein the fluid-arresting structure is in the shape of an aerofoil nose section. 
     
     
       6. The device as claimed in  claim 4 , wherein the fluid-arresting structure is configured to, when the device or aerofoil is exposed to fluid flow, reduce the velocity of fluid entering the duct within an outboard region of the duct to thereby generate the relative high pressure region. 
     
     
       7. The device as claimed in  claim 6 , wherein the fluid-arresting structure comprises a trip strip in the vicinity of the first opening. 
     
     
       8. The device as claimed in  claim 4 , wherein the region of relative high pressure causes the airflow through the duct to have a pressure and velocity imbalance between inboard and outboard sides of the duct within the first restriction and the plenum. 
     
     
       9. The device as claimed in  claim 4 , wherein the duct is configured to have a cross-sectional area profile that causes the region of relative high pressure to adopt an aerofoil shape oriented generally along the longitudinal direction of the duct. 
     
     
       10. The device as claimed in  claim 9 , wherein the region of relative high pressure of aerofoil shape causes part of the airflow through the duct to adopt streamlines that follow said aerofoil shape thereby causing said part of the airflow to adopt a first rotational component. 
     
     
       11. The device as claimed in  claim 10 , wherein the body comprises an intake surface that extends into an inboard wall of the duct, the intake surface being configured to, when the device or aerofoil is exposed to fluid flow, entrain fluid into the duct via the first opening, the intake surface extending generally in an upwards and outboard direction to encourage a part of the fluid flow through the duct to remain attached to the inboard wall. 
     
     
       12. The device as claimed in  claim 11 , wherein the intake surface is contoured so as to cause a part of the fluid flow through the duct along its inboard region to adopt a second rotational component opposite in direction to the first rotational component. 
     
     
       13. The device as claimed in  claim 12 , wherein the duct has a second restriction located between the plenum and the second opening, the second restriction being configured to cause the part of the airflow with the first rotational component to adopt a substantially equal mass flow rate as the part of the airflow with the second rotational component and to direct said parts of the airflow out of the duct via the second opening into the pair of opposing rotating flows. 
     
     
       14. The device as claimed in  claim 3 , wherein the duct has a second restriction located between the plenum and the second opening. 
     
     
       15. The device as claimed in  claim 1 , wherein the first opening is swept relative to a chord line of the body by substantially 5 degrees. 
     
     
       16. The device as claimed in  claim 1 , wherein the body has a first outer surface that encompasses the first opening and a second outer surface that encompasses the second opening, the first and second outer surfaces being cambered so as to, when exposed to fluid flow, generate a first localised region of low pressure outboard of the first opening on the high pressure side, and a second region of low pressure inboard of the second opening on the low pressure side, whereby the first and second low pressure regions pressure balance the pair of opposing rotating flows. 
     
     
       17. The device as claimed in  claim 1 , wherein the body has a leading edge and at least one chord line, the leading edge defining a sweep angle relative to the at least one chord line, wherein the sweep angle between the chord line and leading edge is substantially 24 degrees. 
     
     
       18. The device as claimed in  claim 1 , wherein the centroid of the second opening is positioned outboard and aft relative to the centroid of the first opening. 
     
     
       19. A method for controlling a wake turbulence of an aircraft wing having with a formation at its tip defining a duct extending through the wing from its underside to its upper side, the duct having an inlet on the underside of the wing and an outlet on the upper side of the wing, a plenum between the inlet and the outlet and a restriction between the inlet and the plenum, the duct being configured so that, when the wing is exposed to a free-stream flow, a flow is developed through the duct, the restriction contributes to the formation of a pressure region on the outboard side of the duct in the region of the plenum and a majority of the flow leaving the duct by the outlet is constituted as two counter-rotating vortices, the method comprising subjecting the wing to the free-stream flow so as to cause the said vortices to be generated. 
     
     
       20. An aerofoil comprising a structure for influencing a wake flow of the aerofoil when the aerofoil is subject to fluid flow, the aerofoil having an inboard root end and an outboard tip end, a high pressure side and a low pressure side and a leading edge and a trailing edge, the structure comprising a body located in the vicinity of the tip of the aerofoil, the body having a through-duct with a first opening at a first end of the duct being located on the high pressure side of the aerofoil and a second opening of the duct being located on the low pressure side of the aerofoil, the duct being configured to, when the aerofoil is exposed to fluid flow, permit a fluid flow through the duct to inhibit the flow of fluid around the outboard extremity of the aerofoil and to direct the fluid flow through the duct into a pair of opposing rotating flows of substantially equal magnitude externally of the duct.